This application claims the benefit of the Korean Application No. P2000-84114 filed on Dec. 28, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a driving circuit of a LCD device.
2. Discussion of the Related Art
Generally, an LCD device includes two glass substrates and a liquid crystal layer sealed between them. A thin film transistor (TFT)-LCD is used as a switching element that switches a signal voltage in the liquid crystal layer.
As shown in FIG. 1, the TFT-LCD includes a lower glass substrate 1 provided with a TFT as a switching element, an upper glass substrate 2 provided with a color filter, and a liquid crystal layer 3 injected between the two glass substrates 1 and 2. The TFT-LCD is a non-light-emitting device that obtains an image effect based on the electro-optical characteristics of the liquid crystal layer.
The lower glass substrate 1 includes TFT arrays 4. The upper glass substrate 2 includes a black matrix 5, a color filter layer 6, a common electrode 7, and an alignment film 8.
The lower glass substrate 1 and the upper glass substrate 2 are attached to each other by a sealant 9 such as epoxy resin. A driving circuit 11 on a printed circuit board (PCB) 10 is connected with the lower glass substrate 1 through a tape carrier package (TCP) 12.
A module of the aforementioned LCD includes four elements. The four elements of the LCD module includes a LCD panel with a liquid crystal injected between two substrates, a driver for driving the LCD panel, a PCB provided with various circuit elements, and an external structure having a back light 13.
A driving circuit of a related art LCD device will be described with reference to FIG. 2, which is a block diagram of a related art LCD device.
As shown in FIG. 2, the related art LCD device includes a LCD panel 21, a gate driver 22, a source driver 23, a gamma voltage generator 24, and a timing controller 25. In the LCD panel 21, a plurality of gate lines are arranged to cross a plurality of data lines. A TFT and a pixel electrode are arranged at each crossing portion of the gate and data lines. The gate driver 22 sequentially applies a driving signal to the gate lines. The source driver 23 applies a data signal to the data lines. The gamma voltage generator 24 applies a reference voltage to the source driver 23. The timing controller 25 applies various control signals and voltages to the gate driver 22 and the source driver 23.
In the aforementioned LCD device, light irradiated from a back light (not shown) passes through each of R (red), G (green), and B (blue) color filters in accordance with a voltage applied to each pixel electrode of the LCD panel 21, thereby displaying picture images.
To maintain a stable display quality of the LCD device, an exact and uniform gamma voltage is required. The gamma voltage is generated by a resistance string having a plurality of serially arranged resistors. The gamma voltage is divided to adapt to the transmittivity characteristic of the liquid crystal panel and to obtain a required gray level.
FIG. 3 is a detailed schematic view of the gamma voltage generator of FIG. 2.
The related art LCD device is based on a dot inversion method, in which digital data has 6 bits.
As shown in FIG. 3, the related art gamma voltage generator includes two voltage strings 33 and 35 arranged in parallel between a power source voltage terminal Vdd and a ground voltage terminal Vss, and an amplifier portion 37.
The respective voltage strings 33 and 35 include a plurality of resistors R1-R6 and R7-R12 serially connected to generate a plurality of gamma voltages through voltage division by the respective resistors.
The plurality of gamma voltages generated by the respective voltage strings 33 and 35 are amplified by a corresponding amplifier of the amplifier portion 37. Then the voltages are finally transmitted to the source driver 23.
For example, as shown in FIG. 3, the first voltage string 33 includes six serially connected resistors that outputs five voltage sources V1-V5 through voltage division by the respective resistors. The second voltage string 35 also includes six serially connected resistors that outputs five voltage sources V6-V10 through voltage division by the respective resistors.
The voltage sources V1-V10 are respectively transmitted to an input terminal at one side of a corresponding amplifier, where their noise is removed, and then output to the panel.
In the aforementioned gamma voltage generator, if a power source voltage Vdd is input, gamma voltages from V1 to V10 are set by serially connected resistance values. At this time, gray voltages of a positive frame are set as the voltages from V1 to V5 while gray voltages of a negative frame are set as the voltages from V6 to V10.
Meanwhile, R, G, and B digital data input to the source driver 23, as shown in a waveform of FIG. 4, are converted to analog-type voltage waveforms which will be applied to the LCD panel 21. Then, the converted data are applied to each pixel electrode.
The source driver 23 will be described in more detail with reference to FIG. 5, which is a block diagram of the source driver.
As shown in FIG. 5, the source driver includes a shift register 51, a sampling latch 52, a holding latch 53, a digital to analog (D/A) converter 54, and an amplifier 55.
The shift register 51 shifts a horizontal synchronizing signal through a source pulse clock HCLK and outputs a latch clock to the sampling latch 52.
The sampling latch 52 samples the R, G, and B digital data for each column line (data line) in accordance with the latch clock output from the shift register 51, and then latches the sampled R, G, and B data.
The holding latch 53 latches the R, G, and B data latched by the sampling latch 52 through a load signal LD.
The D/A converter 54 converts the R, G, and B digital data latched by the holding latch 53 to analog signals.
The amplifier 55 amplifies the R, G, and B data converted to analog signals at a certain width and outputs the amplified R, G, and B data to each data line of the LCD panel.
The source driver 23 samples and holds the R, G, and B digital data during 1 horizontal period, converts them to analog data, and amplifies the converted analog data at a certain width. If the holding latch 53 holds the R, G, and B data to be applied to nth data line, the sampling latch 52 samples the R, G, and B data to be applied to (n+1) data line.
The operation of the aforementioned related art driving circuit of the LCD device will be described below.
A video card (not shown) outputs R, G, and B digital data output to input to the source driver 23 without processing. The source driver 23, controlled by the timing controller 25, converts the R, G, and B digital data to analog signals that can be applied to the LCD panel 21, and outputs the resultant values to each data line.
At this time, the gamma voltages obtained by voltage division through resistors are output from the gamma voltage generator 24 to the source driver 23. The gamma voltages are varied depending on the LCD module.
If the gamma voltages are input to the source driver 23, the same voltage is applied to each of R, G, and B pixel electrodes, and the liquid crystal is driven depending on the applied voltage to obtain corresponding brightness of light.
FIG. 6 shows a gray curve obtained by a fixed gamma voltage according to the related art, and FIG. 7 shows a voltage type applied to the LCD panel 21 according to a gray scale by a reference voltage of a gamma voltage generator and a resistor string of the related art source driver 23.
However, the related art driving circuit of the LCD device has several problems.
Among these problems, the related art luminance voltage characteristic does not adapt to variation of peripheral luminous intensity and user""s requests due to a gamma voltage being initially set according to the LCD module. For this reason, a problem arises in that various picture images cannot be displayed.
Accordingly, the present invention is directed to a driving circuit of an LCD device that substantially solves one or more problems due to limitations and disadvantages of the related art.
The invention, in part, provides a driving circuit of an LCD device in which a gamma voltage can be compensated according to a peripheral environment so that exact picture images can be displayed.
The invention, in part, provides a driving circuit of a LCD device that includes a memory dividing the peripheral environment into a plurality of modes and storing information of each mode, an environment sensor sensing variation of the peripheral environment, a controller selecting information of a mode corresponding to the resultant value sensed by the environment sensor, a digital variable resistor adjusting a resistance value to correspond to mode information selected by the controller, and a gamma voltage outputting unit outputting a plurality of gamma voltages corresponding to the resistance value adjusted by the digital variable resistor. An inverter can be connected to the controller. The memory can be an EEPROM.
The invention, in part, pertains to the digital variable resistor and the gamma voltage outputting unit comprising a programmable gamma voltage generator. The memory is provided either outside or inside the programmable gamma voltage generator. When the digital data has 6 bits, then 10 gamma voltages are generated. Also, the gamma voltages are applied to R, G and B pixel electrodes.
In the driving circuit of the LCD device according to the present invention, all of information for the peripheral environment (luminous intensity) are stored, and information corresponding to the current peripheral environment is output to compensate a corresponding gamma voltage, thereby exactly displaying various picture images.
The invention, in part, pertains to a LCD device which has a liquid crystal display and a source driver driving the liquid crystal display. A memory divides a peripheral environment into a plurality of modes and stores information of each mode. An environment sensor senses variation of the peripheral environment, and a controller selects information of a mode corresponding to the resultant value sensed by the environment sensor among information of each mode. An inverter is connected to the controller, and a digital variable resistor adjusting a resistance value to correspond to mode information selected by the controller. A gamma voltage outputting unit outputs a plurality of gamma voltages corresponding to the resistance value adjusted by the digital variable resistor.
The invention, in part, pertains to a method for driving a LCD device, which includes dividing a peripheral environment with a memory into a plurality of modes and storing information of each mode, sensing variation of the peripheral environment with an environment sensor, selecting, with a controller, information of a mode corresponding to the resultant value sensed by the environment sensor, adjusting a resistance value using a digital variable resistor to correspond to mode information selected by the controller, and outputting a plurality of gamma voltages corresponding to the resistance value adjusted by the digital variable resistor, the outputting being performed with a gamma voltage outputting unit.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.